San Bruno Incident Natural Gas Explosion

Following, is an editorial comment from the American Public Gas Association (APGA) regarding the San Bruno, California natural gas explosion and fire on September 9, 2010....

APGA’s thoughts and prayers go out to those who have lost loved ones and homes as a result of this tragic accident.

The National Transportation Safety Board (NTSB) is investigating the cause of the accident, but findings will not be available for weeks or months.

At around 6 pm PDT on September 9, a 30 inch diameter steel natural gas transmission line operated by Pacific Gas and Electric Company ruptured, resulting in a fire that left four dead, three missing and 37 homes destroyed in San Bruno, CA (just west of the San Francisco Airport).

The line was constructed in the 1950’s and since then residential development occurred near the line. Operating pressure at the time of the accident was reportedly 375 pounds per square inch.

While the pipeline was owned by the local distribution company, it is very different from typical distribution piping. Distribution piping operates at much lower pressures and with smaller diameter pipe.

Safety is the #1 priority of APGA member utilities.

Distribution pressures are not high enough to cause a pipe to rupture like the San Bruno transmission pipeline. Ruptures of distribution lines only occur when an outside force such as mechanical excavation breaks the line, and while a break poses grave danger to the excavator and persons and property near the rupture, it cannot cause the widespread damage seen in the San Bruno accident.

The suggestion that a 50+ year old pipeline is less safe than a new pipeline has no basis in fact. Steel does not “age” or lose strength over time. Unless damaged by mechanical equipment or subject to corrosion, steel will retain its original strength.

Utilities go to great lengths to monitor the condition of their pipelines. Steel pipelines are inspected at least once per year for corrosion by measuring the electrical voltage and current flow between the pipe and the soil. Pipelines are checked for leaks using sensitive gas detection instruments at least once every five years (every year in business districts where leaks might migrate under pavement into buildings).

Chemicals are added to natural gas to give it an odor that is readily detectable at levels well below its flammability limit. Despite initial reports that residents had noticed gas odors in the days prior to the accident, the NTSB confirmed that no one notified the utility.

The public can help protect their safety by reporting potential gas odors to the utility and always calling 811 to have buried utilities located before digging.